The other key aspect of the OODA loop as it applies to combat/defense is, make the other person react to YOU as soon as you can, don't just react to THEM. Taking the initiative and making the other person react to you is "getting inside their loop," because it puts them a cognitive step behind you.
Col. Boyd's emphasis wasn't so much on analyzing what occurs at each step of the OODA cycle, but on "getting inside the other person's OODA loop" by doing something that would make them react to YOUR moves instead of remaining a reactive participant in their carefully planned game. Of course, a smart opponent will countermove by trying something else to try to get back inside your loop. But he/she who grabs the initiative, and holds it, has a lot better chance than he/she who remains reactive to someone else's moves.
Scenario 1. You are walking down the edge of a parking lot. You see a person leaning against a car watching you. While you are assessing them as a threat or not, you see them throw down their cigarette and start walking toward you. While you are assessing what to do about that, you notice that there is now a person following you who wasn't there a few seconds ago. Person A is now twenty feet away and asks you if you have some spare change. You start thinking about how to respond to him, when you notice that the guy behind you now has one hand behind his back, and alarm bells are going off, and then the guy in front of you suddenly reaches into his pocket, and...you get the idea. You are behind the curve the whole time, because at every step, THEY are taking the actions and all you can do is react. And maybe they are just asking for change, or maybe they aren't, but the fact is they are controlling the situation and (if their intentions are bad) they have you right where they want you. If they do escalate to force or produce a weapon, you will find yourself behind the curve with assailants on two sides. By putting you constantly in a reactive mode, they keep you off-balance and disoriented.
Scenario 2. You are walking down the edge of a parking lot. You see a person leaning against a car watching you. While you are assessing them as a threat or not, you see them throw down their cigarette and start walking toward you. While you are assessing what to do about that, you notice that there is now a person following you who wasn't there a few seconds ago. Person A is now twenty feet away and asks you if you have some spare change. Instead of remaining a passive participant, you quickly cut between two parked cars and over to the next row. They react by looking at each other, then moving to follow, signaling that their intent is questionable. You then decide further action is warranted and dash to the next row, but cutting in front of that parked SUV that obscures their view of you for a second and heading back for the store. They react by picking up their pace but are now stacked on one side of you. You pull a can of OC from your pocket; they notice, or don't, and react; if they advance, you spray and run, if they don't advance, you keep moving toward the store, or whatever. The point is, you are no longer reacting to them; you managed to turn the tables such that they are reacting to you, putting you a step ahead of them, keeping them off-balance.
